Emulsion nonuniform

Figure 13. The effect of nonuniform polymerization on the expansion behavior of carboxylic emulsion polymers. The power feed example was prepared using the monomer feed profile illustrated in Figure 12 ((%) uniform feed power feed).

Wall temperatures Some practitioners of the art and sdence of emulsion polymerization believe that nonuniform wall temperatures can play a role in wall polymer formation. The reaction in any deposit could be faster if the temperature is higher. Thus, some reactors are designed with cooling jackets that cover as much of the reactor as possible, inclnding the reactor top. 

Raman fibre optics has been used to study the emulsion homopolymerisations of styrene and n-butyl acrylate (35). An IR spectroscopic technique for the examination of radical copolymerisations of acryl and vinyl monomers was developed. A comparative study of the copolymerisation of model monomer pairs was made using monofunctional and polyfunctional compounds. The data established the role of structural-physical transformations, involved in the formation of crosslinked polymers, on the copolymerisation kinetics and on the nonuniformity of distribution of crosslinks in the copolymers formed (151). Raman fibre optics of polymerisation of acrylic terpolymers was also used to monitor as well as an on-line measurement of morphology/composition (66). The high temperature (330 °C) cure reaction of 4-phenoxy-4 -phenyl-ethynylbenzophenone was monitored using a modulated fibre optic FT-Raman spectrometer (80). 

Fig. 4.60A plots the standard deviation of concentration in time which indicate that the very low standard deviation of concentration is obtained for the initial period, where CO2 is suddenly injected into the column, and the bubble is detached from the distributor (without gas exchange with the emulsion phase). Afterward, N2 from the emulsion phase dilutes the bubble, leading to an increased standard deviation, until the end of the evolution. The standard deviation approaches the plateau at i = 0.11 s, when about 50% of CO2 inside the bubble is replenished by N2. For time longer than i= 0.11 s, the concentration decreases slowly, due to the diffusion contribution. Fig. 4.60 shows that the concentration inside the bubble during the phase exchange is nonuniform. This means that, once the concentration in the emulsion phase can be detected, a more detailed model should be used to elucidate the gas exchange between bubble and emulsion. For the scope of this chapter, a simplified method is used. 

A special drop mixing problem arises with the suspension polymerization of vinyl chloride. Because the monomer is very reactive and has a high enthalpy of polymerization, operators are reluctant to mix initiator in the monomer before a suspension is formed. Therefore, as a safety precaution, the initiator is often dispersed in the aqueous phase of a stabilized suspension. Then the subsequent mixing of monomer and initiator can be quite slow. Zerfa and Brooks [61, 62] showed that many monomer drops remained uninitiated when monomer in other drops had polymerized to a considerable extent. That did not happen when initiator was dissolved in the monomer before it was dispersed see Figure 5.5. This nonuniformity in drop behavior affected the final polymer properties. Also, addition of initiator via the aqueous phase promoted simultaneous emulsion polymerization and modified the PSD. Drop mixing rates were quantified by using dyed monomer... 

Multiphase polymer particles prepared by emulsion polymerizations find a number of important commercial applications such as elastomers, coatings, adhesives, and impact resistant thermoplastics. Latex products, which exhibit nonuniform particle morphology, are produced when two or more monomers react with one another such that separate polymer phases form during emulsion polymerization. The incompatibility of different polymers or the sequence and location of the formation of polymers can result in separate polymer phases. 

This chapter serves as an introduction to the origin of nonuniform latex particles. First, a brief discussion of the seeded emulsion polymerization technique that has been widely used to prepare composite polymer particles with a variety of morphological structures is given. This is followed by the illustration of the effects of important factors such as initiators, monomer addition methods, polymer molecular weight, volume ratio of the second-stage monomer to the seed polymer, and polymerization temperature that affect the morphological structures of latex particles. The development of morphological structures of nonuniform latex particles will then be covered at the end of this chapter. 

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